The field of the present invention relates to methods and apparatus for drilling a hole in a ground formation. In particular, apparatus and methods for drilling a hole in an unconsolidated ground formation (earth, back fill, or other medium) and advancing a casing therethrough are described herein that employ a ring bit, a center bit, and a casing shoe.
A wide variety of apparatus and methods are available for drilling a hole in a ground formation. Some of these are described in:
U.S. Pat. No. 5,511,628 entitled “Pneumatic drill with central evacuation outlet” issued Apr. 30, 1996 to Ardis L. Holte;
U.S. Pat. No. 5,787,999 entitled “Drill bit with set of underreamer arms” issued Aug. 4, 1998 to Ardis L. Holte;
U.S. Pat. No. 5,803,192 entitled “Drill bit retainer for a down hole hammer assembly” issued Sep. 8, 1998 to Ardis L. Holte;
U.S. Pat. No. 5,957,226 entitled “Reverse circulation drilling system with hexagonal pipe coupling” issued Sep. 28, 1999 to Ardis L. Holte;
U.S. Pat. No. 5,975,222 entitled “Reverse circulation drilling system with bit locked underreamer arms” issued Nov. 2, 1999 to Ardis L. Holte;
U.S. Pat. No. 6,209,665 entitled “Reverse circulation drilling system with bit locked underreamer arms” issued Apr. 3, 2001 to Ardis L. Holte; and
U.S. Pat. No. 6,394,197 entitled “Reverse circulation drilling system with bit locked underreamer arms” issued May 28, 2002 to Ardis L. Holte.
Each of the above-named patents are hereby incorporated by reference as if fully set forth herein.